Project Summary/Abstract An overarching goal of cognitive behavioral therapies (CBTS) is to improve skill acquisition (i.e. the ability to successfully perform a skill learned in treatment) and skill utilization (i.e. the frequency with which a patient practices or employs therapeutic skills). However, many patients receiving CBT fail to achieve sufficient rates of skill utilization or adequate skill acquisition and treatment outcomes suffer as a result. Augmentations to CBT that improve skill utilization and acquisition could result in substantial improvements in treatment outcome for a variety of mental health disorders. Ecological momentary interventions (EMIs) are a promising method for improving skill utilization and acquisition in CBT. EMIs provide assistance when and where individuals are most in need (typically through smartphone applications). Smartphone-based EMI systems now have the capability to deliver interventions at the precise moment when these interventions are most needed using algorithm-based context-aware systems. An EMI system designed to increase skill utilization and acquisition could 1) detect when a patient should practice using a therapeutic skill and 2) provide a tailored interventions designed to facilitate skill use at the time when receiving an intervention would be most impactful. Despite the increased development and widespread use of both smartphone app technologies and EMI systems, there currently exists limited data to suggest whether smartphone-based EMI systems can successfully improve skill acquisition and utilization when used as an adjunct to in-person CBT. Patients with bulimia nervosa (BN), a disorder characterized by recurrent episodes of binge eating and purging imposed on top of an otherwise highly restrictive diet, may represent an ideal group to test the utility of a skills-based EMI system. We chose to augment CBT for BN for three reasons: (1) Symptom improvement in CBT for BN can be explained by improvements in a relatively small number of concrete and measureable therapeutic skills, (2) acquisition and utilization of these skills is often poor in CBT for BN and poor skill acquisition and utilization is strongly related to treatment failure, and (3) the barriers to skill acquisition and utilization in CBT for BN are likely addressable by EMI augmentation. In the current study, we propose to develop, refine, and test an EMI system (CBT+) that will use data collected from standard CBT for BN electronic self-monitoring forms to identify when patients should use CBT skills. In Phase 1, we will develop CBT+ (based on prior EMI-systems developed by our team) and will use an iterative development approach (n=10) to ensure CBT+ achieves acceptable target engagement. Using a single-case ABAB design (A= EMI on, B= EMI off), we will evaluate the ability of CBT+ to 1) increase utilization of six core skills in CBT for BN during ?EMI on? phases and 2) produce more rapid gains in skill acquisition during ?EMI on? phases. In Phase 2, we will complete a pilot RCT (n=45) comparing standard CBT for BN (n=15) to CBT for BN augmented with CBT+ (n=30) to assess the feasibility and acceptability of CBT+ and evaluate target engagement and validation.